Annual Summary Document Template*
1. Cover Page (1 page):
 Group list:
1. Dr. Toșa Valer: senior researcher physicist, project leader;
2. Dr. Bende Attila: senior researcher physicist;
3. Dr. Kovács Katalin: young researcher physicist;
4. Dr. Fălămaș Alexandra: young researcher physicist.
 Specific scientific focus of group:
The main research domain of the group involved in this project is studying the
interaction of powerful ultrashort laser pulses with atomic and molecular systems. We
also study by numerical modeling the macroscopic effects caused by the propagation of
such laser pulses in gaseous media: partial of complete ionization of the medium in the
optical electric field, which causes rapid variation of the medium’s refractive index,
which in turn strongly affects the temporal/spectral and spatial shape of the propagating
pulse itself.
 Summary of accomplishments in the last year:
The main objective of the project is to ensure the control of the ELI laser pulse
temporally, spectrally and spatially, during its propagation, from generation to the target.
The task for year 2014 was to establish a framework method that can be adapted for the
complete characterization of laser pulses (in temporal and/or spectral and spatial domain)
in any given point of the beam path. In order to accomplish this task the following steps
were performed: both the Hankel transform method used for beam propagation in free
space and through linear optical elements, and the method based on the solution of the
wave-equation used in the case of beam propagation in ionized media were modified to
match the experimental characteristics of the ELI-NP project, namely: long propagation
distances, low atmospheric pressure, high field intensities, specific focusing geometry.
We discussed with the designers of the future beamline about the potential location(s)
and envisioned method(s) for pulse diagnostic and have set the basis for potential
configurations regarding the pulse characterization and the method for processing the
experimental data.
*
Please fill in all the required items and do not alter the template
2. Scientific accomplishments (max. 3 pages) – Results obtained in the last year.
The purpose of the present project as a whole is to offer a reliable numerical calculation tool for
ELI-type beam characterization and diagnostics throughout all the stages of beam shaping and
transport, especially at points where experimental measurements are difficult or impossible to be
performed.
In these first 6 months we designed a general framework, a strategy to approach the problem
constructively at the so early stage of implementation of the ELI-NP infrastructure that even those
collaborators directly involved in the ELI-NP beamline design are not sure yet about the real
parameters and geometrical structure. The implemented strategy can be schematically represented
in a graph:
Fig. 1. Schematic representation of a possible route where the proposed method can be exploited
Method 1. We suppose that right after the exit from the compressor an experimental pulse
characterization measurement can be performed. In the above graph this step is represented by a
beam splitter that deviates a small part of the pulse and the measurement can be done. Depending
on the diagnostic method, one can obtain the pulse description in the time domain, i.e. the amplitude
A(t), pulse energy E and pulse duration (FWHM) . Basically, the same information can be
extracted also in spectral domain, i.e. spectral amplitude A() and phase ( plus the pulse energy
and duration. The pulse being now fully described, it can be transported according to the
peculiarities of the whole infrastructure, given that the beam goes through linear optical elements
only. The first method implemented in this project (call it Method 1.) is based on the Hankel
transform. With this diffraction integral the pulse shape in the far-field can be calculated if the pulse
A
B
shape in near-field is known and the ray matrix  C D is also known which contains the


propagation through all linear optical elements. The Hankel transform propagates every frequency
component independently:

a
2
 
i
ikS
E
(
r
,
z
,
)


E
(
r
,
z
,
)
e
r
dr
d

1

1
1
1
1
1
1


B
0
0



, where
12
2
S

z
Ar

2
r
r
cos(

)

Dr
1
1
1
2
B
.
In the equations E is one spectral component of the beam, a is its radial dimension. This form of
the Hankel transform is angle-dependent, which is an advantega in cases when the measured beam
shape is strongly assymetric in radial direction. Otherwise, in case the pulse is (almost) radially
symmetric, one can integrate over the angle 1 and obtain:


2


Dr
a
2
ikAr


ik
z

1


2
i
krr
2
B


1


2
B
E
(
r
,
z
)


e
E
(
r
,
z

0
)
e
J
r
dr


1
1
1
0
1
1

B 0
B




.
In the equations A, B, C, D are the ray-matrix elements which may be frequency dependent,
therefore the dispersion is included in this treatment.
The advantage of this Method 1. is that it can be easily adapted to the changing geometry affecting
the beam path, it is only needed to accordingly modify the ray-matrix elements, and make sure all
new optical elements remain linear.
It is the ideal case when after the linear propagation the pulse could be characterized experimentally
once more, and the measured pulse shape could be compared with the calculated one.
Method 2. After the amplification stages, the ELI-NP laser pulse reaches extremely high intensities,
since this is the purpose of the whole big project. The propagation of a femtosecond laser pulse of
such high intensity induces strong nonlinear response of the medium, therefore pulse propagation
cannot be treated anymore with Method 1. In this case the pulse propagation can be described by
the wave equation which is derived from Maxwell’s equations:


2
1

E
(
r
,
z
,
t
)2 2
2
1

E
(
r
,
z
,
t
)


(
1

)
E
(
r
,
z
,
t
)
1
1
2 2
2 eff
c

t c
.
The strongly nonlinear effects induced in the medium due to the presence of a strong laser pulse are
found in the rapid variation of the effective refractive index of the medium: the rising edge of a
strong laser pulse induces the nonlinear variation of the refractive index, and the trailing edge of the
same pulse already is encountering this changed refractive index. It is then obvious that the
effective refractive index varies both in time and space, and reads:
2
(
n
,
r
,
z
,
t
)
p
e
(
n
,
n
,
r
,
z
,
t
)

(
n
)

(
n
)
I
(
r
,
z
,
t
)
2
eff
a
e
0
a
2
0
2 .
Here the dispersion due to the neutral atoms (na density), the optical Kerr-effect (nonlinear
refractive index caused by laser intensity I) and the plasma dispersion (ne electron density) are
included.
In order to solve the wave equation, the completely defined pulse at the entrance to the nonlinear
propagation region must be known, either in spectral or in time domain. If there is a possibility to
experimentally diagnose the pulse at this position, it would be the most reliable starting point for
calculations. However, if this is not possible anymore, the outcome from the linear propagation
stage (see Method 1.) is the input for Method 2.
Further on, in the focal region where the pulse should reach unprecedented extreme intensities, any
direct diagnosis is excluded. On the other hand, during the light pulse interaction with any form of
matter it is crucially important to know the exact shape of the interacting light pulse. At this point
the calculations are the only possible method to estimate what is in the hot interaction region.
Even if the propagation of the extremely strong pulses in is vacuum, the pulse will interact with the
residual atomic or molecular gas in the vacuum tube. Due to the extreme pulse intensity, probably
all the atoms/molecules will be completely ionized, therefore a non-negligible plasma density will
be created which in turn influences the pulse shape itself. Method 2. is meant to describe pulse
distortions in these conditions.

 

Since the ELI-NP infrastructure is in projection phase yet, the main achievement of this project
PULSE-PROPAG in year 2014 was to build a general framework of the methods to be exploited
such that the real experimental conditions to be relatively easy to incorporate.
3. Group members (table):
 List each member, his/her role in project and the Full Time Equivalent (FTE) % time in
project. The FTE formula to be used is: FTE = Total number of worked hours in the last
year/1020 hours†;
Nr.
crt
Name
Position (cf.
HG 475/2007)
1
Tosa Valer
CSI
2
Bende Attila
CSI
3
Kovacs Katalin
CSIII
4
Falamas Alexandra
CS
Role in the project
Project leader. He is the author of the main computer code used for the
calculations. Modifies parts of the code such to be suitable to treat the
specific configurations to be implemented in ELI-NP.
Senior researcher, has expertise in ab-initio calculations. He calulates the
ionization rates of the molecular gases residually present in the beam
transport tubes in the ELI-NP infrastructure. Due to the extremely high
laser intensities the atoms and molecules will be completely ionized.
Has expertise in modeling the propagation of electromagnetic pulses in
ionized media and modeling the interaction of short pulses with atoms.
She uses the computer code to model different possible beam transport
and diagnostics configurations relevant to the future ELI-NP
infrastructure
Young researcher, has experitse in experimental laser beam
characterization and diagnostics. She provides the modeling-team the
practical information regarding the bottlencks in the characterization of
powerful laser pulses, and suggests the possible places and methods for
beam diagnostics.
Full Time
Equivalent
0.11
0.09
0.11
0.09
4. Deliverables in the last year related to the project:
 List of papers (journal or conference proceeding):
1. M. Negro, M. Devetta, D. Facciala, A.G. Ciriolo, F. Calegari, F. Frassetto, L. Poletto,
V. Tosa, C. Vozzi, and S. Stagira, Non-collinear high-order harmonic generation by
three interfering laser beams, Optics Express 22, 29778 (2014)
 List of talks of group members (title, conference or meeting, date);
1. Falamas A. My laser experience presented at the Summerschool “Lasers in Medicine
and Life Sciences”, 14.7-25.07.2014 Szeged, Hungary
2. Tosa V. Single attosecond pulses in water window from synthesized waveforms,
presented at ECLIM 2014, 31.08-05.09.2014, Paris, France
5. Further group activities (max. 1 page):
 Collaborations, education, outreach: we continue also within this project our well
established collaboration with INFLPR and ELI-NP Magurele, as well as with the
University of Szeged.
6. Financial Report for the last year (see the Annex).
7. Research plan and goals for the next year (max. 1 page).
The main objective of project PULSE-PROPAG for year 2015 is the development of the numerical
software which we will use to simulate pulse propagation in any given conditions and media.
There is at least one major problem to be solved at this stage, namely the calculation of the
ionization rates of atoms when they are fully ionized. Because of the extreme laser intensities
planned for ELI-NP, all the residual atoms in the vacuum tubes will be fully ionized. So far, in most
of the cases the atoms in interaction with strong electromagnetic pulses were singly ionized, and
†
1020 hours = 170 average monthly hours x 6 months
there are well-known methods to calculate the ionization rates (for ex. ADK method). For the ELIpulses these methods are obsolete, extended multiple ionization rates need to be calculated.
We will follow this research plan in 2015:
First we determine the temporal characteristics from the spectral characteristics, and the spatial
characteristics during the propagation from the generation point to the target. Next, we calculate the
characteristics of the pulse during propagation and as a function of the residual pressure in the
transport chamber. Certainly, we will need to optimize the calculation method, then perform several
“virtual experiments” for the simulation of the propagation of the pulse in configurations specific to
ELI-NP.
We mention that the whole project PULSE-PROPAG is designed to support the ELI-NP project in
the design and construction of the beamline, therefore a continuous communication with those
colleagues who are involve in ELI-NP is essential.
Annex
Financial Report
according to the regulations from H.G. 134/2011
lei
2014
Value
Type of expenditures
Planned
1
2
Realized
PERSONNEL EXPENDITURES, from which:
33739
33746
1.1. wages and similar income, according to the law
26389
27469
7350
6277
229
586
2.1. capital expenditures
0
0
2.2. stocks expenditures
0
361
229
225
1.2. contributions related to salaries and assimilated
incomes
LOGISTICS EXPENDITURES, from which:
2.3. expenditures on services performed by third
parties, including:
....
3
TRAVEL EXPENDITURES
2389
2025.31
4
INDIRECT EXPENDITURES – (OVERHEADS) *
9089
9088.69
45446
45446
TOTAL EXPENDITURES (1+2+3+4)
* Specify the rate (%) and key of distribution (excluding capital expenditures).
To be filled in for:
- the project leader;
- for each of the parteners (if any);
- for the whole project.
Project leader,
Dr. Tosa Valer
Date:
28.11.2014